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Possible mortality benefit from sun exposure

Abstract

This is an interesting study in that it highlights potential benefits of sun exposure .This needs to be tempered with the known risk of increased skin cancers .

The Potential Dangers of Sun Avoidance

We are all aware of the damaging consequences of spending too much time in the sun. New research is now shifting the focus on the harmful effects of sun underexposure.

A recent study published in the Journal of Internal Medicine suggests that avoiding sun exposure can be just as, if not more dangerous than spending too much time in the sun.

The study estimated that sun avoidance was a risk factor for death of all causes of the same magnitude as smoking.

The Swedish study, conducted in a group of 20,000 women between age 25 and 64 found that compared to those with active sun exposure, women who avoided sun exposure completely had a 60% increased risk of death from cardiovascular disease. This cohort also had an increased risk of death from non-cancer illness.

The study authors categorised the women in four groups based on their reported sun exposure from total sun avoidance to moderate and most-active exposures. The study followed these women for 20 years and recorded their mortality rates and cause of death.

Life expectancy was reduced in 50 and 60 year olds who avoided the sun by approximately 0.6 and 1.3 years compared with the highest sun exposure during the 20 years of follow up. The majority of this was due to an increased rate of death from cardiovascular disease, as well as other, non-cancer deaths. The highest sun exposure group had higher rates of cancer death but had lower overall mortality rates.

While the study cannot determine causation between sun avoidance and death, the study reports a correlation that is dose-dependent, with the highest sun exposure group having the lowest death rates overall and this increasing as sun exposure decreased.

One of the weaknesses of the study was that it was not able to differentiate between the positive effects of other healthy lifestyle factors such as exercise and sun exposure. Were the women who reported to be spending more time in the sun healthier because they spent time in the sun exercising for example?

Despite these questions, there are plausible, biological explanations for why sun avoidance may be harmful. For example, light hitting the retina signals the production of melatonin in the brain, a dysfunctional melatonin receptor has been linked to impaired insulin release, increasing the risk of type 2 diabetes. Sun avoidance may decrease melatonin and this may have consequences on insulin function. Vitamin D (increased in the body by sun exposure) is thought to play an important role in fighting infection in the body, particularly in respiratory tract infections. Sun exposure has also been observed to have positive effects on blood pressure, help release endorphins which reduces stress and might decrease the development of atherosclerotic plaques which can lead to heart attacks and strokes.

The positive effects of sun exposure by no means counteract the significantly increased risk of skin cancer than UV radiation causes. Particularly in New Zealand, it is important to spend time in the sun responsibly, using sunscreen and spending time in the shade to avoid sunburn. This study suggests that total sun avoidance may do more harm than good.

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